Data storage and retrieval today rely heavily on microfiche recording of the data. Alphanumeric characters are phtographically reduced so that a printed page occupies a space of less than one centimeter square on the microfiche medium. By thus compressing approximately 200 printed pages into an area of approximately 3".times.5", the space required to store the data is drastically reduced.
Data is recorded on a microfiche by sequentially exposing different portions of the film to the different pages of printed data. To accomplish this, a piece of microfiche film (usually from a roll) is held horizontal in a platen which may then be moved in a rectilinear fashion over a horizontal reference plate having an optical aperture through which page images are projected onto the film.
A satisfactory microfiche recorder must provide highly accurate registration of the film to ensure reliable data retrieval. In particular, perpendicularity of the rows and columns in which the reduced pages are arranged must be maintained in order to ensure that the microfiche can be properly read on microfiche readers. Also, the film must be precisely held in a plane so that defocusing of the projected images does not occur. This is especially critical if the microfiche is to be used as a master for producing copies.
The microfiche recorder must also be able to perform the film movement over the reference plate in a rapid manner. This is clearly essential when large volumes of data are to be transcribed, as in the case when computer output is being recorded on microfiche. It can also be seen that a microfiche recorder must be able to operate with a minimum amount of maintenance in order to ensure that intolerable backlogs of data to be recorded do not occur.
A typical prior art microfiche recorder is disclosed in U.S. Pat. No. Re. 29,254 to Kahle, et al. In that patent, platen movement is accomplished by means of mutually perpendicular lead screws driven by servo motors, and drive nuts on the platen. An arrangement making use of lead screws has several difficulties. A certain amount of backlash is virtually unavoidable in a lead screw drive system. This leads to inaccuracies in the registration of the platen, and may result in undesirable vibrations when the platen undergoes the relatively large accelerations that occur. Additionally, the lead screws tend to constrain vertical movement of the platen so that its removal for cleaning, inspection, etc. is rendered difficult, thereby increasing maintenance time. In addition, it is necessary to maintain critical parallelism and mutual perpendicularity between the lead screws and the guide rails which control the movement of the platen, since any misalignment can cause excessive wear and aggravate existing blacklash and misalignment problems.
A further difficulty with prior art microfiche recorders is that no provision is made for decoupling the platen from the driving means when the platen undergoes excessive acceleration or deceleration. In certain malfunction situations, the platen can be driven with great force against stationary portions of the apparatus. Platen damage as well as damage from shock transmitted to the drive system can occur.
In order to provide for rapid platen movement, the mass being moved should be kept to a minimum. Failure to do this can result in excessive strain on the driving system, or the requirement of unduly large and powerful components. Prior art microfiche recorders, in an effort to eliminate film misalignment and twisting problems have sometimes resorted to mounting the film supply rigidly to the platen. Although this can greatly facilitate the alignment of the film and its handling, it also adds substantially to the mass that must be repeatedly accelerated.